Production of titanium



March 26, 1957 B. B. RANEY 2,786,808

PRODUCTION OF TITANIUM Filed Sept. 22, 1954 M a u MOLENHfiL/DE INVENTORnited States Patent PRODUCTION OF TITANIUM Ben B. Raney, Linton, Ind.,assignor to Chicago Development Corporation, Riverdale, Md.

Application September 22, 1954, Serial No. 457,760

7 Claims. (Cl. 204-10) This application is a continuation-in-part of myapplication, now abandoned, Serial No. 230,336, filed June 7, 1951, forProduction of Titanium Powder.

In said application the production of finely divided titanium by passinga periodically reversed direct current between titanium electrodesimmersed in a fused alkali or alkaline earth metal chloride bath Wasdisclosed.

I have found that the process of this invention is applicable to othermetals and alloys.

The use of two similar electrodes with periodic reversals has manyadvantages over the use of one soluble and one insoluble electrodewithout reversals: there is no problem of contamination of the depositedmetal by the cathode, and no problem of removal of the deposited metalfrom the cathode.

The process of the present invention is especially valuable in theproduction of powders from alloys. In this connection the production ofalloy powder by the process of my earlier invention may, in someinstances, yield a composition differing from that of the anode becauseof a diiference in the diffusion rates of the metal halides formed atthe anode. In the process of the present invention the alloy powderformed is of the same composition as that of the metallic portion of thealloy electrodes. This is the result of the formation and reductionprocesses being separated by only a short time interval during whichdifilerential diifusion of the metal halides is insignificant.

My process is also of particular utility in preparing comminutedmaterial from alloys or metals which become passive when made an anodein an electrolytic cell containing fused alkali or alkaline earthhalides. This passivity is observed, for example, in tungsten metal andin certain alloys of nickel-chromium and iron-nickelaluminum cobalt. Themechanism of passivation in the case of these alloys has not beenestablished beyond a doubt; however, it apears highly probable that thepassivity results from a slow rate of diifusion of one or more of thehalides formed at the anode so that a high resistance film is formed onthe anode. Alloys which have this passivation phenomenon cannot beetfectively comminuted by an electrolytic process using the procedure ofmy earlier invention; in the cases of such alloys periodic reversal ofthe direct current is necessary.

The frequency of reversal ofthe current in my present invention varieswidely, in accordance with the result which it is desired to accomplish.In general, the higher the frequency the better the results. Frequenciesof a few reversals per second may be used; however, in general Icontemplate using reversal frequencies within the range of from aboutone per second to about one per five minutes. Alternating currents withreversals of many cycles per-second are not satisfactory. 7 There areseveral factors which affect the particle size of the metal powderproduced. Fine particle size results from the precipitation of metalfrom a dilute solu tion of the metal halide by a solution of alkali oralkaline earth metal formed in the cathodic portion of the cycle.

2,786,808 Patented Mar. 26, 1957 The higher the frequency of currentreversal the less chance of dilution of the halide formed in the anodicportion of the cycle and the larger the particle size.

Important electrorefining can be effected by the use of my presentinvention. Impurities, including oxygen and nitrogen in the transitionelements like titanium and zirconium and metallic solutes more noblethan the metal being refined, which remain in the residual anode anddifluse therein, can be recovered in the anode skeleton remaining afterthe electrolysis procedure has been effected. To prevent the solution ofthe more noble metals the potential of the anode against the solutionmust be made as low as possible. This is accomplished by adjusting thecurrent density so that during the anodic portion of the cycle thepotential of the anode measured against an unpolarized electrode of thesame material is not more than 0.1 volt anodic. Under these conditionscoarse powders of pure metal form at the electrodes and fall to thebottom of the cell from which they can be removed. The impurities, asnoted, can be recovered in the anode skeletons.

The temperature and the composition of the electrolyte are matters ofsome importance. In general, the higher the temperature the coarser thepowder. The electrolyte can be any fused chloride or bromide of alkaliand alkaline earth metals. For metals or alloys which are readilyoxidized the electrolyte must be free from oxygen and the cell must beprotected from the air. I have found that sodium chloride gives largerparticles and better refining than other halides of the group. Sodiumchloride also has the advantage of being soluble in water withouthydrolysis so that it can be removed from the metal product withoutcontamination of the latter.

My invention is applicable to the production of alloy powders from awide variety of metals and alloys. It is, of course, essential that themetals or alloys be solid at the temperature of the fused salt used andthat the chlorides or bromides formed be reducible by alkali and/oralkaline earth metals.

For electrorefining purposes my present invention is particularlyapplicable to titanium and zirconium containing oxygen.

Having described my invention, I will now illustrate it by examples.

Example I In this example, I used two titanium electrodes and reversedthe direction of current flow from time to time so that both electrodeswere consumed and reduced to powder. In this way I prevented anypossible contamination of the titanium with the metal of the pot. Inthis example I used a sillimanite crucible with an inverted nickel belldipping into a fused mixture of 40 mol. percent of commercial lithiumchloride, balance potassium chloride. The construction of the apparatusfor this example is illustrated in the single figure of the appendeddrawing which is a diagrammatic representation of one form of apparatusoperable forcarrying out theherein process. In the drawing, '1 is asillimanite pot, 8 is the nickel bell, electrodes 2 and-2 are massivetitanium bars, 3 and 3 are packing glands, '4 and 5 are a helium inletand a helium outlet, respectively, and 7 and 7 are insulating washers.Electrical connections were made to the titanium rods through thepacking glands. The temperature of the bath was maintained at about 400C.

Electrolysis began with 2.7 volts, and the current density wasapproximately 1 ampere per square inch. The current direction wasreversed every five minutes. titanium bars were evenly attacked and thetitanium powder produced was approximately 1 gram per ampere 'hour. Itwill be seen from calculation thatthis corre sponds to the solution anddeposition of the titanium in bivalent form. Electrolysis could becontinued without loss of efliciency until the suspended titanium powderamounted to 8% of the weight of the electrolyte.

' Example II I proceededasin Example lexceptthat I used massive titaniumcontaining a :niinor but significant amount of oxygen as :theelectrodes. The electrolyte in this example consisted :essentiallyofoxygen-free sodium chloride. The temperature wasmaintained .atapproximately 850 C., and the current density at 1-000 amperes persquare foot. The cell contents were protected by an atmosphere of inertgas. The reversals were at -a frequency o-r' one per second. 'Thevoltage was volt, approximately .2 of which corresponded to the IR dropin the electrolyte. Electrolysis was continued until residualmetal oneach electrode was 20% of the original. The titanium sank to the bottomof the cell in theform of coarse particles of titanium of high purity.These particles when :fusedin an inert-atmosphere had a 'Brinellhardness of 80.

Example 111 I proceeded as in Example 11 except that-l used massivezirconium containing oxygen. The :product was pure .coarsefparticles ofzirconium.

Example IV :In this examplel used electrodes of Alnico," an alloy ofiron, aluminum, nickel and cobalt. The electrolyte was a mixture ofsodium chloride =and potassium-chloride, the temperature was about 800C.; the current density 600 amperes per square foot; reversals, everyfive seconds; voltage 6.0 volts. The-powdered alloy product wasrecovered from the bottom of the 'cell. The magnetic properties of thispowder showed that it was a uniform alloy of the same composition andproperties as those of the massive material from which the electrodeshad been formed.

Example V In this experiment Example IV was repeated except 7 that theelectrodes were formed of Nic'hrome V, and the voltage was 4.5. Themetal powder product Was a uniform alloy of the same composition andproperties as those of the massive material.

Example VI Iron electrodes are immersed in a molten bath of lithiumchloride and potassium chloride at 400 C. Reversals occur every fiveminutes. Iron powder remains in suspension, and the particles are mostlysub micron in size.

Molybdenum powder has been produced by the carrying out of thisprocess,which latter is operable also for preparing powders of aluminum, copper,uranium, and a wide variety of other metals more noble than thealkalinous metal employed in the fused salt bath. As was mentionedabove, the process has unique applicability to the production ofcomminuted alloys of the Nichromeelectrodes each being formed of ametallic material selected from the group consisting of titanium,zirconium, tungsten, nickel-chromium alloys and Alnico, said electrodesbeing immersed in a molten electrolyte consisting essentially of atleast one halide salt of the group consisting of chlorides and bromidesof alkalinous metals, said molten bath being maintained at a temperatureat which said alkalinous metal salt is molten but below the meltingpoint of the metallic electrodes, the reversal frequencies being withinthe "range of from about one per second to about one per five -minutes,whereby to obtain said metallic material, in comminuted form, dispersedin the molten electrolyte.

2. Process as defined in claim 1, in which the current density ismaintained at a value greater than 1 ampere per square inch.

3. Process as defined in claim 1, which the anode potential ismaintained at a value not substantially exceeding 0.1 volt anodic.

4. A process for producing a purified comminuted metal from impureimassive metal selected from the group consisting of titanium andZirconium, "which includes the steps -of passing "a periodicallyreversed direct current between two electrodes of the -massi-ve metalimmersedin .a' fus'ed bath -consisting otat le'as't'one halide selectedfrom the group consisting of alkali and alkaline earth metal chloridesand bromides, the reversals in current direction being between one persecond and one per :five minutes, whereby to form e'ornmin'uted puremetal dispersed in the fused bath.

5. process for producing oxygen-free comminu'ted metal fromoxygen-containing metal selected from the group consisting of titaniumand zirconium, which includes the steps of passing a periodicallyreversed direct current between two electrodes of the massive metalimmersed in a fused bath consisting of at least one halide selected fromthe group consisting of alkali and alkaline earth metal chlorides andbromides, the reversals in current direction being between one persecond and one per five minutes, whereby to form comminuted pure metaldispersed in the fused bath.

6. .Process of producing ductile, substantially pure titanium 'incomminuted form from a massive material consisting essentially oftitaniumfcontaining a minor but significant amount of an impurityrendering the same relatively non=ductile, which comprises passingunidirectional 'direct current between two electrodes formed of saidmassive material, said electrodes being immersed in an oxygen-freem'olten electrolyte in "an electrolytic cell, said electrolyteconsisting essentially of an alkalinous metal chloride maintained at atemperature above the melting point of said chloride but below that ofsaid electrodes, continuously reversing the current direction at afrequency of from 'one reversal per second to one reversal per fiveminutes during the electrolysis, maintaining a current density such thatduring the anodic portion of the cycle the potential of the anodemeasured against an unpolarized electrode of the same material is notsubstantially more than 0.1 volt anodic, terminating the passage ofperiodically reversed current before the electrodes have ceased to beself-supporting but after a substantial amount of particulate titaniumof high purity has been formed and has sunk to the bottom of the cell,and thereafter recovering the so-formed particulate titanium from the'cell contents.

7. Process of producing ductile, substantially oxygenfree titanium incornminuted form from a massive material consisting essentially oftitanium containing a minor but significant amount of oxygen, whichcomprises passing a unidirectional current between two electrodes formedof said massive material, said electrodes being immersed in anoxygen-free molten electrolyte con- 1 sisting essentially of sodiumchloride maintained at a temperature of approximately 850 C. in anelectrolytic cell, continuously reversing the current direction at afrequency of approximately one reversal per second during theelectrolysis, maintaining a current density, of approximately 1000amper'es per square foot, such that References Cited in the file of thispatent UNITED STATES PATENTS Slepian Jan. 2,

Fisher Oct. 1,

Kroll Dec. 31,

Schultz et a1. Feb. 14,

FOREIGN PATENTS Great Britain May 24,

France Dec. 30,

1. PROCESS OF PRODUCING COMMINUTED METALLIC MATERIAL WHICH COMPRISES THESTEPS OF PASSING A PERIODICALLY REVERSED UNIDIRECTIONAL DIRECT CURRENTBETWEEN TWO SIMILAR ELECTRODES EACH BEING FORMED OF A METALLIC MATERIALSELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, TUNGSTEN,NICKEL-CHRONIUM ALLOYS AND "ALNICO," SAID ELECTRODES BEING IMMERSED IN AMOLTEN ELECTROLYTE CONSISTING ESSENTIALLY OF AT LEAST ONE HALIDE SALT OFTHE GROUP CONSISTIN OF CHLORIDES AND BROMIDES OF ALKALINOUS METALS, SAIDMOLTEN BATH BEING MAINTAINED AT A TEMPERATURE AT WHICH SAID ALKALINOUSMETAL SALT IS MOLTEN BUT BELOW THE MELTING POINT OF THE METALLICELECTRODES, THE REVERSAL FREQUENCIES BEING WITHIN THE RANGE OF FROMABOUT ONE PER SECOND TO ABOUT ONE PER FIVE MINUTES, WHEREBY TO OBTAINSAID METALLIC MATERIAL, IN COMMINUTED FORM, DISPERSED IN THE MOLTENELECTROLYTE.